March - 2011

  The circuit board for the 3 Amp Booster on this page has been replaced by a newer version. The new circuit will have fewer parts and use a larger, one-piece heat sink.

2011 - 3 Amp DCC Booster

  All other functions and features remain the same.

2009 - 3 Amp - DCC Track Booster (LMD18200)

  The DCC booster shown on this page uses a LMD18200 motor driver H-bridge IC. The booster's designed output rating is 3 amps at 15 volts.

  This booster was developed from the one shown on the My MiniDCC© System page at this site.

3 Amp DCC Booster Circuit Features

3 Amp DCC Booster Circuit Notes

3 Amp DCC Booster Schematic

  The following diagram shows the schematic for the circuitboard for the 3 Amp DCC Booster.

  NOTE: The variable resistor R12 shown on the schematic is an optional component and would only be installed if an overload current of less than 3 amps was needed. See the Optional Overload Setting Adjustment section below for further details.

  The value of resistor R11 may change depending on the particular LMD18200 used in a given circuit.

Power Supplies For This Booster

  The DCC Booster circuit will be damaged if the polarity of the power supply is reversed. Care must be taken when connecting a power supply to the circuitboard.

  A suitable power supply for this circuit from Skycraft Parts & Surplus - 15 VDC 4.5 Amp, Switching Type.

Optional Overload Setting Adjustment

  This booster circuit is designed to have a fixed, overload current setting of between 3.2 and 3.5 amps.

  The variable resistor R12 shown on the schematic would only be used if a lower overload current setting. Under normal operating conditions the position of R12 is short circuited by a path on the circuitboard.

  If a lower overload setting is desired, the shorting path can be cut and R12 adjusted as needed.

  The formula for calculating the boosters overload setting is: 0.467V / (R11 + R12) / 377μA = Amps DC.

  The value 0.467V (volts) is the gate threshold voltage of the SCR formed by transistors Q1 and Q2. This value was determined by experimentation.

  The value 377μA (microamps) is the 'Current Sense Output' (pin 8) output per amp of load current in amps as given in the LM18200's datasheet.     ( 377μA = 377 X 10-6 Amps )

  NOTE: The actual output from the Current Sense Output pin 8 may be higher or lower than that specified in the LMD18200's datasheet. Therefore, resistor R11 may need to be tailored to the actual conditions of the circuit.

  A DC ammeter with a 3 amp or greater capacity connected between the POSITIVE output of the power supply and the PLUS input of the booster circuit can be used to set the trip point while the booster is under load.

  * - The value of resistor R11 may change depending on the particular LMD18200 used in a given circuit.

Return to the Main Page

Please Read Before Using These Circuit Ideas

  The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.

  If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.

  Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.

Return to the Main Page

January, 2013