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When using an H bridge IC such as L293 which has enable inputs, is it possible to tie outputs together such that an 'enabled' output is joined to a 'disabled' output without ill effect? In the system I am thinking of (to do with DCC Train control) there would never be a time when both tied outputs would be enabled but could be a time when neither was enabled. Is this possible? (or harmfull to the IC?)

I am very new to this website so don't know how to add schematic. However, what I want to do is to use this device to power a point (turnout) section of track in a model railway using DCC. In one position of the turnout I want to power the frog with one output(say the A side) with the other tied output (B side) disabled and then in the other position of the turnout the power comes from the B side with the A side disabled.

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    \$\begingroup\$ What does the datasheet say? \$\endgroup\$ – Ignacio Vazquez-Abrams Aug 13 '16 at 13:19
  • \$\begingroup\$ What problem are you trying to solve with this "solution"? Can you post a schematic? (Schematic button on editor toolbar if you want to create one with the relevant bits.) \$\endgroup\$ – Transistor Aug 13 '16 at 13:33
  • \$\begingroup\$ If it's a DC system then surely you just want to connect the frog alternately to V+ or COM (common)? \$\endgroup\$ – Transistor Aug 13 '16 at 17:34
  • \$\begingroup\$ You can add schematics as images as well. \$\endgroup\$ – Bence Kaulics Aug 13 '16 at 17:35
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The 'frog' is that area in the centre of a set of railway points (British) or switch (North American) where the rails intersect. It presents a problem on DC model railways as it can short out the supply when the points are being switched.

enter image description here

Figure 1. Frog polarity control. Source: New Railway Modellers.

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 2. Alternating polarity to each section of track using half H-bridge drivers. 'A' and 'B' are two halves of a H-bridge driving the upper and lower rails of Figure 1. The FROG connection drives the frog.

The switches of Figure 2 represent the transistors of a semiconductor bridge driver.

In the system I am thinking of (to do with DCC Train control) there would never be a time when both tied outputs would be enabled but could be a time when neither was enabled. Is this possible? (or harmfull to the IC?)

If you disable the frog before switching the points and then re-enable it you should be fine. No damage will occur. It would be best to have a current limited supply to prevent damage to the H-bridges in the event of a short circuit which could happen due to other reasons anyway.

Some of your concerns are discussed in the New Railway Modellers link above.

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