3 Amp - DCC Track Booster - 2011 (LMD18200)

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

3 Amp Booster Circuit Features

  * - If this booster continuously carries more than 2.5 amps (83% of maximum), a larger booster should be considered or more power districts should be created.

3 Amp DCC Booster Circuit Notes

3 Amp DCC Booster Schematic

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

  NOTE: The variable resistor R10 shown on the schematic is an optional component and would only be installed if an overload current of less than 3 amps is needed. See the Optional Overload Setting Adjustment section below for further details.

  The value of resistor R11 may need to be adjusted depending on the particular LMD18200 used in a given circuit. (390 ohms has been suitable in every case thus far.)

Power Supplies For This Booster

  This circuit is designed to make use of surplus - 15 volt, 3 amp laptop power supplies.

  Used laptop power supplies can be can be purchased inexpensively at many computer and electronics recycling facilities. (Have them tested before purchasing.) These supplies are also available through many other sources as well.

  An example of a suitable power supply for this circuit is from Skycraft Parts & Surplus - 15 VDC 4.5 Amp, Switching Type.

Basic Circuit Board External Connections Diagram

With Increased Overcurrent Delay

  Adding a 33 to 100 microfarad capacitor at the external RESET terminals of the circuit board will slow the response of the overcurrent trip circuit and make the booster less sensitive to brief short circuits.

3 Amp DCC Booster Parts List

CIRCUIT PART NUMBER - PART - Qty - Digi-Key Number
IC 1 - 6N137 - 1 - 6N137QT-ND
IC2A, B, C, D - LM339 - 1 - LM339NFS-ND
IC 3 - LMD18200 - 1 - LMD18200T-ND
IC 4 - L7805 - 1 - 497-1009-ND
Q1 - 2N3904 - 1 - 2N3904FS-ND
Q2 - 2N3906 - 1 - 2N3906FS-ND
- - - - - - -
D1, 3, 4, 6 - 1N4148 - 4 - 1N4148DICT
D2 - 3mm GREEN LED - 1 -  
D5 - 3mm RED LED - 1 -  
D7 - 3mm YELLOW LED - 1 -  
- - - - - - -
R1, 3, 5, 6, 8, 13, 14, 15, 16 - 10K - 9 - 10KQBK-ND
R2, 4, 12 - 470 Ohm - 3 - 470QBK-ND
R7 - 22K - 1 - 22KQBK-ND
R9 - 1K - 1 - 1.0KQBK-ND
R10 - 1K Pot - 0 -  
R11 - 390 Ohm * - 1 - 390QBK-ND
R17 - 2.2K - 1 - 2.2KQBK-ND
- - - - - - -
C1, 2, 5 - 2.2uF/35V - 3 - P5175-ND
C3 - 10uF/35V - 1 - P5178-ND
C4 - 0.1uF/63V - 1 - BC1095CT-ND
C6 - 2200uF/25V - 1 - P5158-ND
C7, 8 - 0.01uF/63V - 2 - BC1101CT-ND
- - - - - - -
Terminal Block - 2 Position 5mm - 2 - ED1623-ND
Terminal Block - 2 Position 3mm - 2 - ED2635-ND
HEAT SINK - For LMD18200 - 1 - HS343-ND
S1 - N.O. Push Button - 1 - SW400-ND

  * - The heat sink shown in the photo of the circuit board is not identical to the one in the parts list but they have the same capacity.

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

Driving This Booster From The Output Of Another

  It is possible to drive this booster from the output of an existing booster. There will be a very small shift in the phase of the second and subsequent boosters but this should not cause problems.

  The input to the second booster should come directly from the output terminals of the existing booster to minimize any signal degradation or noise.

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 R10 shown on the schematic would only be used if a lower overload current setting. Under normal operating conditions the position of R10 is short circuited by a path on the circuit board.

  If a lower overload setting is desired, the shorting path can be cut, R10 added to the circuit board and adjusted as needed.

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

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

  The value of 377μA (microamps) is the 'Current Sense Output' (pin 8) output per amp of load current 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.

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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.

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03 April, 2016