Products and Services for Embedded Systems

Prototyping System for ZiLOG Z8 Encore!®
Power Supply

The Prototyping System main board requires input power either at 5 volts DC regulated or at between 6 and 16 volts DC unregulated.  The ZiLOG power pack is a suitable power source.  Operation from four NiMH cells is also expected to be possible.  Power can be applied to the board via a 2.1 mm center-positive coaxial jack or a user-supplied hookup.  Linear regulators produce on-board supplies of 3.3 volts (VDD) and 5 volts (VCC).

Power Supply Option Kit

The table below lists the parts required for a medium current 5 volt and 3.3 volt on-board regulated power supply plus a power indicator LED.  You will also require an external DC power source.  The power pack included with the ZiLOG Development Kit Z8ENCORE000ZCO is suitable for this purpose.

If kitting for yourself, you can economize by using cheaper, low current regulators, omitting the power indicator LED and/or using a regulated 5 volt power source so that the 5 volt regulator and associated capacitors are not needed.  For a 3.3 volt only system, several components are omitted.  Technical details are provided below.

For a higher current power supply, you will need heatsinks on the regulators and/or higher current regulators.  If the regulators do not provide short-circuit and over-current protection, fuses are recommended.  Suitable self-reparing fuses by Raychem are available from Mouser (catalog 616, page 353).  For example, stock # 650-RUE090 has a hold current of 0.9 A and is priced at $0.56.

Order Kit from ECROS Technology

A Power Supply Option Kit is available from ECROS Technology including all parts in the table above.

Note: due to the weight of wall-wart power supplies, an additional $3.00 will be added to shipping charges for each that you order.

Click this button for general ordering information, shipping charges, tax, etc.

Power Supply Assembly Tips

Aluminium electrolytic capacitors must be installed with the correct polarity.  The holes into which the postive and negative leads must go are marked on the PCB silkscreen.  The negative lead of the capacitor is usually shorter than the positive lead.  In addition, the case carries a black band on the side of the negative lead.

The LED must be installed with the correct polarity.  The cathode lead must go in the hole closer to the main prototyping area and the anode lead must be closer to the reset switch.  The cathode lead is shorter than the anode lead.

Power Supply Technical Details

Various build options allow for regulators of different current capability, including vertically-mounted TO220 regulators with heatsinks.  The current available from these regulated supplies will vary according to which build option is selected and the maximum input voltage applied to the board.  The table below gives estimates of available current to the user (in addition to the currents taken by the microcontroller, display, serial interface, etc.).

† The LF33CV and LF50CV regulators supplied by ECROS Technology in the Power Supply Option Kit are internally limited to a maximum current of 500 mA each.  Other regulators should be substituted is higher currents are required (but see Regulator "Drop Out" Voltage, below).

Unregulated Power Sources

The full schematic of the Prototyping System main board power supply is shown below:

This power supply is designed for inputs of between 6 and 16 volts, giving considerable flexibility in the choice of power source.  All components can be selected from many alternatives, some of which you may have in your spares drawer.  ECROS Technology can supply a Power Supply Option Kit.  The parts in this kit have been chosen as a compromise between price and performance.

Capacitors C13 and C15 are necessary for stability of the regulators.  The value shown of 0.1µF is suitable for the option package parts, but larger values would be fine too.  For different regulators (U5 and U6), consult the manufacturer's data sheet.

The values of capacitors C12 and C14 can be chosen according to how much current you will draw and whether you are switching the current, for example to drive a relay.  Holes are provided in the main board to accept the lead pitches of a wide range of common axial electrolytic capacitors.  Do not get these capacitors the wrong way round!  Positive and negative are clearly marked on the silkscreen.

Fuses F1 and either F2 or F3† can be installed for protection in the event of accidental short circuits or other over-current conditions.  The regulators in the option package have internal over-current protection and the fuses can be replaced with insulated wire links.  When substituting regulators without built-in protection, consider using fuses such as Raychem self-repairing fuses (Mouser catalog 616, page 353).

† Whether fuses or wire links, only one of F2 and F3 should be installed, the other must be open circuit.  Install F2 and leave F3 open to derive the 3.3 volt power directly from the input power.  This is the recommended configuration.  If you want the 3.3 volt power to be derived from the 5 volt power, install F3 and leave F2 open.  You might chose this option if you are drawing a lot of power at 3.3 volts and almost nothing at 5 volts.  Heat dissipation in the 3.3 volts regulator is reduced.

Regulated 5 Volt Power Sources

If the Prototyping System is to be operated from a 5 volt regulated supply, U5 must be omitted from the main board and replaced with an insulated wire link between its IN and OUT terminals (marked I and O on the silkscreen).  Fuse (or wire link) F2 should be used and F3 left open.  C12 may be omitted if the power source has a sufficienly low AC source impedance or includes its own decoupling capacitor.  It is recommended that C13 be installed.  U6 must be chosen to have a "drop out" voltage low enough to ensure proper operation at the minimum expected input voltage, see below.

Regulator "Drop Out" Voltage

When substituting regulators, watch out for the "drop out" voltage.  This is the voltage by which the input must exceed the output for proper regulation.  The regulators selected by ECROS Technology have low drop out voltages of 0.7 volts at 500 mA and 0.35 volts at 200 mA.  By contrast, the popular and inexpensive 7805 regulator, although capable of twice the current, has a drop out voltage of 2 volts.  The difference between the input voltage and the regulated voltage must not go below the drop out voltage or regulation will degrade.

Take, for example, the situation in which the input is regulated to a nominal 5 volts and U5 is bridged with a wire (see above).  Suppose the actual input can fall by 5% to 4.75 volts.  The drop out voltage of U6 must be no greater than 4.75 - 3.3 = 1.45 volts.

A 3.3 Volt Only Supply

The 5 volt supply is used by the Display Option Package and the EIA-232-D driver/receiver in the Serial Option Package Kit.  If you are not using these options and have no other need for 5 volts, you can omit U5, C12, C12 and F1.  To distribute 3.3 volts on VCC as well as VDD, install an insulated wire link between any pair of VCC and VDD access points, for example in the block to the right of the main expansion connector.  A pin-for-pin replacement of the EIA-232-D driver/receiver is available which will operate from 3.3 V.

Addtional Power or Other Voltages

Additional regulators can be placed in the user areas to supplement the on-board regulators or to create other regulated voltages (subject to available input power).  All PCB traces on the main board carrying power supplies to expansion connectors and the connectors themselves are capable of carrying at least one amp.

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