Hi, I'm looking for an IC for an old Radio Shack burglar alarm system. Radio Shack tells me they can't fix the system as the IC is bad and they cannot locate a replacement. Any help would be appreciated. Thanks, Bruce
Looking for an IC L78MGSKE
Feb 24, 2006
4 Replies
On 24 Feb 2006 08:29:25 -0800, "Bruce" put finger to keyboard and composed:
The L78MG is a Sanyo 4-terminal adjustable regulator. I'm betting it is similar to a uA78MG or uA78MGU1C which are both subbed by an NTE953:
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$File/L78MG.pdf
Should these parts be unsuitable, it should be a simple matter for any competent technician to adapt one of many standard regulators for this circuit.
- Franc Zabkar
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You can replace it with a 3 terminal LM317 regulator: ------- ------- | o | / L78MG | Pins: 1 = Vin = LM317 Vin |_______| | | 2 = Gnd not needed /_______/| ------- 3 = Output = Vout |LM317 || | | | | 4 = Control =* Adj |_______|/ 1 2 3 4 | | | Adj | Vin Vout
The circuit on pin 4 of the L78MG is not identical to the circuit on the adjust pin of the LM317. You will need to know what voltage the L78MG is supposed to provide. The voltage out of the LM317 is set with a
240 ohm resistor connected from Vout to Adj, and a 5K trimpot connected from Adj to ground. You'll wire it like this: 1) Remove the LM78G and install wires from holes 1 & 3 that it occupied to the LM317 pins, as shown-------- ------- | o | / L78MG | (removed) |________| | | /________/| ------- | LM317 || | | | | |________|/ 1 2 3 4 | | | | | | +-----+ Adj | Vin | | | | | | Vout | | | Gnd---+---[POT]---[240R]---+ | | | | | | | +------------------------------------------+ | | | +--------------------------------------------------+
You adjust the 5K pot to give you the same voltage that the L78MG gave you before it died.
Ed
(diagram snipped)
Not quite; the 240R resistor goes between the Adj pin and the Vout pin, with the pot going from Adj to earth.
See
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for a datasheet with suggested applications.
Though I'm surprised you can't get a 78MG; maybe the shop just can't be bothered, hoping you'll buy a new unit.
rgds
LAurence
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Thanks! Here's the corrected diagram:
-------- ------- | o | / L78MG | (removed) |________| | | /________/| ------- | LM317 || | | | | |________|/ 1 2 3 4 | | | | | | +-----+ Adj | Vin | | | | | | Vout | | | Gnd---+---[POT]----+---+ | | | | | | | | | [240R] | | | | | | | | +-----------------------------------+------+ | | | +--------------------------------------------------+
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